METHOD: Add a tincture of food colouring to a small amount of water pour into ice 'cube' tray and freeze. Fill martini glass with water (or else vodka if authenticity is a concern). Stir gently, don't shake. Await first moments of melting, ensuring the ice continues to slowly spin, until leakage of the coloured water occurs and grab shot, quickly - do not hold breath whilst awaiting the decisive moment.

Unexpectedly, but happily, a degree of separation takes place between the food colouring and the water as the food-coloured water freezes. The pure water then melts more slowly than the food coloured water which allows the coloured water 'leaking' effect to take place.. I should have expected this as impurities are known to affect the freezing and boiling points of water.